The present invention relates to improvements in a spin-polarization detector for measuring the spin polarization of an electron beam, and more particularly to a spin-polarization detector which is small in size and high in sensitivity, and which is suited to measure the spin polarization of electrons emitted from a solid body such as secondary electrons, reflected electrons, photo-electrons, thermal electrons, and electrons generated by field emission.
In a Mott detector which is widely used for measuring the spin polarization of an electron beam, it is required to count up electrons which are scattered back from a heavy atom target, in a region applied with a high voltage. Accordingly, in a conventional Mott detector, as described in, for example, Japanese laid-open patent publication No. JP-A-59-187,281 and Japanese Journal of Applied Physics Vol. 23, No. 3 March, 1984 pp. L187-L188, an electron detector, a pre-amplifier, a linear amplifier and a light emitting diode are arranged in a region applied with a high voltage so that one electron incident on the electron detector is converted by the electron detector, the pre-amplifier and the linear amplifier into one electric-pulse and the electric pulse is converted by the light emitting diode into light pulse, the light pulse from the light emitting diode travels through an optical guide to a light receiving element kept at the ground potential, to be converted in an electric pulse, and the electric pulse thus obtained is measured.
Further, in the prior art, a sheet of heavy metal foil is used as a scattering target, and back-scattered electrons from the foil are detected to calculate the spin polarization of an electron beam incident on the foil.
In the above prior art, however, there arise the following problems.
(1) In the high-voltage region, a weak output signal from the electron detector is amplified and shaped, and then converted into the light pulse. Accordingly, it is required to dispose in the high-voltage region an electronic circuit system including the electron detector, the pre-amplifier, the linear amplifier and the light emitting diode. Further, it is necessary to supply electric power to the electronic circuit system disposed in the high-voltage region. Hence, the Mott detector is complicated in structure, high in manufacturing cost, and large in size. Further, owing to the heat generation of each of circuit elements constituting the electronic circuit system, this system has a limited life.
(2) Only one sheet of foil is used as the scattering target. Accordingly, the greater part of an electron beam incident on the foil passes through the foil, and a very small number of electrons are scattered back from the foil, to be received by the electron detector. Thus, the detecting efficiency is not high.